Rubber Composition for Conveyor Belt, and Conveyor Belt

ABSTRACT

A rubber composition of the present technology for a conveyor belt contains a diene rubber and a carbon black, the diene rubber containing: a natural rubber; and a modified butadiene rubber obtained by modifying a butadiene rubber with a nitrone compound; the content of the natural rubber in the diene rubber being 30 to 85 mass %, and the content of the modified butadiene rubber in the diene rubber being 15 to 70 mass %.

TECHNICAL FIELD

The present technology relates to a rubber composition for a conveyorbelt and a conveyor belt.

BACKGROUND ART

A conveyor belt is used for transportation of materials and the like,and as the transportation volume increases, demands in improvement indurability (tear resistance, bending resistance and the like) haveincreased in recent years.

Meanwhile, in order to improve transportation efficiency, a conveyorbelt as long as several kilometers in length is also introduced in themarket. Accordingly, the power consumption is also increasing.Therefore, a conveyor system with good energy-saving properties is alsoin demand. Furthermore, there is an increase in demand for a conveyorbelt in cold regions. Thus, good energy-saving properties are alsorequired at low temperatures, such as approximately −40° C. That is,good energy-saving properties are required for a wide range oftemperatures (for example, −40 to 20° C.).

As a rubber composition used for production of a conveyor belt, JapaneseUnexamined Patent Application Publication No. 2008-38133A discloses “arubber composition for a conveyor belt comprising a rubber componentincluding a natural rubber (NR) and a poly-butadiene rubber (BR), acarbon black and the like”. In addition, Japanese Unexamined PatentApplication Publication No. 2008-38133A discloses that energyconsumption can be reduced by using such a rubber composition for aconveyor belt.

Under these circumstances, the present inventors have studied a rubbercomposition for a conveyor belt containing a natural rubber, a butadienerubber and a carbon black using Japanese Unexamined Patent ApplicationPublication No. 2008-38133A as a reference. The study lead the presentinventors to realize that energy-saving properties, tear resistance, andbending resistance of the conveyor belt obtained requires furtherimprovement considering the increased level of demand for the futuretransportation efficiency and durability.

SUMMARY

The present technology provides: a rubber composition for a conveyorbelt, the rubber composition exhibiting exceptional energy-savingproperties, tear resistance, and bending resistance when made into aconveyor belt; and a conveyor belt in which such a rubber compositionfor conveyor belt is used.

As a result of diligent research, the present inventors discovered thatenergy-saving properties, tear resistance, and bending resistance of theconveyor belt can be improved by blending a modified butadiene rubber,which can be obtained by modifying a butadiene rubber with a nitronecompound, at a predetermined ratio.

Specifically, the inventors discovered that the improvements toenergy-saving properties, tear resistance, and bending resistance of theconveyor belt can be achieved by the following features.

(1) A rubber composition for a conveyor belt containing: a diene rubberand a carbon black,

the diene rubber containing:

a natural rubber; and

a modified butadiene rubber obtained by modifying a butadiene rubberwith a nitrone compound;

the content of the natural rubber in the diene rubber being 30 to 85mass %, and the content of the modified butadiene rubber in the dienerubber being 15 to 70 mass %.

(2) The rubber composition for a conveyor belt according to (1)described above, wherein the nitrone compound contains a carboxy group.

(3) The rubber composition for a conveyor belt according to (1) or (2)described above, wherein the content of the carbon black is from 20 to50 parts by mass per 100 parts by mass of the diene rubber.

(4) The rubber composition for a conveyor belt according to any one of(1) to (3) described above, wherein a nitrogen adsorption specificsurface area of the carbon black is from 25 to 100 m²/g.

(5) The rubber composition for a conveyor belt according to any one of(1) to (4) described above, wherein the nitrone compound is a compoundselected from the group consisting ofN-phenyl-α-(4-carboxyphenyl)nitrone,N-phenyl-α-(3-carboxyphenyl)nitrone,N-phenyl-α-(2-carboxyphenyl)nitrone,N-(4-carboxyphenyl)-α-phenylnitrone,N-(3-carboxyphenyl)-α-phenylnitrone, andN-(2-carboxyphenyl)-α-phenylnitrone.

(6) The rubber composition for a conveyor belt according to any one of(1) to (5) described above, wherein a degree of modification of themodified butadiene rubber is from 0.02 to 4.0 mol %, where “degree ofmodification” refers to the proportion (mol %) of double bonds modifiedwith the nitrone compound to all the double bonds contained in thebutadiene rubber.

(7) A conveyor belt comprising the rubber composition for a conveyorbelt described in any one of (1) to (6) described above as a lower coverrubber layer.

As described below, according to the present technology, a rubbercomposition for a conveyor belt and a conveyor belt can be provided,where the rubber composition for a conveyor belt is the rubbercomposition exhibiting exceptional energy-saving properties, tearresistance, and bending resistance when made into a conveyor belt; andthe conveyor belt is a conveyor belt in which such a rubber compositionfor conveyor belt is used.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a cross-sectional view schematically illustrating a preferredembodiment of the conveyor belt of the present technology.

DETAILED DESCRIPTION

Hereinafter, a rubber composition for a conveyor belt and a conveyorbelt comprising the rubber composition for a conveyor belt of thepresent technology will be described.

In this specification, a numerical range represented using “(from) . . .to . . . ” refers to a range including the numerical values statedbefore and after the “ . . . to . . . ” as a lower limit value and anupper limit value.

Rubber Composition for a Conveyor Belt

The rubber composition of the present technology for a conveyor belt(referred to as a composition of the present technology hereinafter aswell) contains a diene rubber and a carbon black, the diene rubbercontaining: a natural rubber; and a modified butadiene rubber obtainedby modifying a butadiene rubber with a nitrone compound; the content ofthe natural rubber in the diene rubber being 30 to 85 mass %, and thecontent of the modified butadiene rubber in the diene rubber being 15 to70 mass %.

It is conceived that, since the composition of the present technologyhas such a constitution, the composition exhibits excellentenergy-saving properties, tear resistance and bending resistance whenformed into a conveyor belt. Although the reason is not clear, it isassumed to be as follows.

As described above, the composition of the present technology contains amodified butadiene rubber obtained by modifying a butadiene rubber witha nitrone compound. In such a composition, the nitrone-modified portionin the modified butadiene rubber interacts (bonds) with a carbon blackin the composition. Thus, energy loss due to friction between the rubberand the carbon black during bending can be suppressed. Supposedly,energy-saving properties of the conveyor belt made from the compositionare excellent as a result.

Additionally, because the nitrone-modified portion in the modifiedbutadiene rubber interacts with a carbon black in the composition asdescribed above, dispersion of the carbon black is improved, resultingin an improved uniformity of the belt conveyor obtained. Supposedly,tear resistance and bending resistance are improved as a result.

Each component contained in the composition of the present technologywill be described in detail hereinafter.

Diene Rubber

A diene rubber used in the composition of the present technologycontains a natural rubber and a modified butadiene rubber obtained bymodifying a butadiene rubber with a nitrone compound. The content of thenatural rubber in the diene rubber is 30 to 85 mass % and the content ofthe modified butadiene rubber in the diene rubber is 15 to 70 mass %.

The diene rubber may contain a rubber component other than a naturalrubber and the modified butadiene rubber. Such a rubber component is notparticularly limited, but examples include an isoprene rubber (IR), abutadiene rubber (BR), an aromatic vinyl-conjugated diene copolymerrubber (e.g. styrene-butadiene rubber (SBR)), an acrylonitrile-butadienecopolymer rubber (NBR), a butyl rubber (IIR), a halogenated butyl rubber(Br—IIR, Cl—IIR), and a chloroprene rubber (CR). Of these, a butadienerubber (BR) is preferable.

Natural Rubber

The diene rubber contained in the composition of the present technologyincludes a natural rubber.

The content of the natural rubber in the diene rubber is 30 to 85 mass%. If the content of the natural rubber is out of the range above, theenergy-saving properties or tear resistance and bending resistance areinsufficient.

Nitrone-Modified Butadiene Rubber

As described above, a diene rubber used in the composition of thepresent technology contains a modified butadiene rubber obtained bymodifying a butadiene rubber with a nitrone compound (referred to as anitrone-modified butadiene rubber hereinafter in some cases).

Butadiene Rubber

A butadiene rubber used for production of a nitrone-modified butadienerubber is not particularly limited.

A butadiene monomer used for production of the butadiene rubber is notparticularly limited and the examples include 1,3-butadiene, and2-chloro-1,3-butadiene. Among these, 1,3-butadiene is preferably used. Asingle butadiene monomer may be used alone, or a combination of two ormore butadiene monomers may be used.

From the viewpoint of handling, the butadiene rubber described abovepreferably has a weight average molecular weight (Mw) of from 100,000 to1,500,000, and more preferably from 300,000 to 1,300,000. In the presentdisclosure, the weight average molecular weight (Mw) is measured by gelpermeation chromatography (GPC) using tetrahydrofuran as a solvent, andcalibrated using standard polystyrene.

Nitrone Compound

A nitrone compound used for production of a nitrone-modified butadienerubber is not particularly limited, as long as it is a compound having anitrone group represented by Formula (1) below.

In Formula (1), * indicates a bond position.

The nitrone compound is preferably a compound represented by Formula (2)below.

In Formula (2) above, X and Y each independently represent an aliphatichydrocarbon group, an aromatic hydrocarbon groups or an aromaticheterocyclic group, optionally having a substituent.

Examples of the aliphatic hydrocarbon group represented by X or Yinclude alkyl groups, cycloalkyl groups, and alkenyl groups. Examples ofthe alkyl group include a methyl group, an ethyl group, a n-propylgroup, an isopropyl group, a n-butyl group, an isobutyl group, asec-butyl group, a tert-butyl group, a n-pentyl group, an isopentylgroup, a neopentyl group, a tert-pentyl group, an 1-methylbutyl group, a2-methylbutyl group, an 1,2-dimethylpropyl group, a n-hexyl group, an-heptyl group, and a n-octyl group. Among these, alkyl groups havingfrom 1 to 18 carbons are preferable, and alkyl groups having from 1 to 6carbons are more preferable. Examples of the cycloalkyl group include acyclopropyl group, a cyclobutyl group, a cyclopentyl group, and acyclohexyl group. Among these, cycloalkyl groups having from 3 to 10carbons are preferable, and cycloalkyl groups having from 3 to 6 carbonsare more preferable. Examples of the alkenyl group include a vinylgroup, an 1-propenyl group, an allyl group, an isopropenyl group, an1-butenyl group, and a 2-butenyl group. Among these, alkenyl groupshaving from 2 to 18 carbons are preferable, and alkenyl groups havingfrom 2 to 6 carbons are more preferable.

Examples of the aromatic hydrocarbon group represented by X or Y includearyl groups, and aralkyl groups.

Examples of the aryl group include a phenyl group, a naphthyl group, ananthryl group, a phenanthryl group, and a biphenyl group. Among these,aryl groups having from 6 to 14 carbons are preferable, aryl groupshaving from 6 to 10 carbons are more preferable, and a phenyl group anda naphthyl group are even more preferable.

Examples of the aralkyl group include a benzyl group, a phenethyl group,and a phenylpropyl group. Among these, aralkyl groups having from 7 to13 carbons are preferable, aralkyl groups having from 7 to 11 carbonsare more preferable, and a benzyl group is even more preferable.

Examples of the aromatic heterocyclic group represented by X or Yinclude a pyrrolyl group, a furyl group, a thienyl group, a pyrazolylgroup, an imidazolyl group (an imidazole group), an oxazolyl group, anisooxazolyl group, a thiazolyl group, an isothiazolyl group, a pyridylgroup (a pyridine group), a furan group, a thiophene group, apyridazinyl group, a pyrimidinyl group, and a pyrazinyl group. Amongthese, pyridyl groups are preferable.

The substituents that may be included in the group represented by X or Yis not particularly limited and examples thereof include an alkyl grouphaving from 1 to 4 carbons, a hydroxy group, an amino group, a nitrogroup, a carboxy group, a sulfonyl group, an alkoxy group, and a halogenatom. Among these, carboxy groups are preferable.

Note that examples of the aromatic hydrocarbon group having such asubstituent include aryl groups having a substituent, such as a tolylgroup and a xylyl group; and aralkyl groups having a substituent, suchas a methylbenzyl group, an ethylbenzyl group, and a methylphenethylgroup.

The compound represented by Formula (2) above is preferably a compoundrepresented by Formula (3) below.

In Formula (3), m and n each independently represent an integer from 0to 5, and a sum of m and n is 1 or greater.

The integer represented by m is preferably an integer from 0 to 2, andmore preferably an integer 0 or 1, because solubility to a solventduring nitrone compound synthesis is better and thus synthesis easier.

The integer represented by n is preferably an integer from 0 to 2, andmore preferably an integer 0 or 1, because solubility to a solventduring nitrone compound synthesis is better and thus synthesis easier.

Furthermore, the sum of m and n (m+n) is preferably from 1 to 4, andmore preferably 1 or 2.

Carboxynitrone represented by Formula (3) is not particularly limited,but is preferably a compound selected from the group consisting ofN-phenyl-α-(4-carboxyphenyl)nitrone represented by Formula (3-1) below,N-phenyl-α-(3-carboxyphenyl)nitrone represented by Formula (3-2) below,N-phenyl-α-(2-carboxyphenyl)nitrone represented by Formula (3-3) below,N-(4-carboxyphenyl)-α-phenylnitrone represented by Formula (3-4) below,N-(3-carboxyphenyl)-α-phenylnitrone represented by Formula (3-5) below,and N-(2-carboxyphenyl)-α-phenylnitrone represented by Formula (3-6)below.

The method of synthesizing the nitrone compound is not particularlylimited, and conventionally known methods can be used. For example, anitrone compound having a nitrone group may be obtained by stirring acompound having a hydroxyamino group (—NHOH) and a compound having analdehyde group (—CHO) at a molar ratio of hydroxyamino group to aldehydegroup (—NHOH/—CHO) of 1.0 to 1.5 in the presence of an organic solvent(for example methanol, ethanol, and tetrahydrofuran) at room temperaturefor 1 to 24 hours to allow the both groups to react.

Method of Preparing Nitrone-Modified Butadiene Rubber

The method for modifying a butadiene rubber with a nitrone compound isnot particularly limited. Examples of the method include blending thebutadiene rubber described above and the nitrone compound at atemperature of 100° C. to 200° C. for 1 to 30 minutes.

When blended as such, a cycloaddition reaction occurs between the doublebond of the butadiene rubber and the nitrone group in the nitronecompound, forming a five-membered ring as illustrated in Formulas (4)and (5) below. Note that Formula (4) below represents a reaction betweena double bond of a butadiene rubber with 1,4 bond and a nitronecompound, and Formula (5) below represents a reaction between a doublebond of a butadiene rubber with 1,2 bond and a nitrone compound.Formulas (4) and (5) illustrate the reactions for the case where thebutadiene is 1,3-butadiene, but the reactions for the case where thebutadiene is a butadiene other than 1,3-butadiene also gives a fivemembered ring via a similar reaction.

Here, the amount of the nitrone compound that reacts with the butadienerubber is not particularly limited, but preferably from 0.1 to 10 partsby mass and more preferably from 0.3 to 5 parts by mass, per 100 partsby mass of the butadiene rubber.

Degree of Modification

The degree of modification of the nitrone-modified butadiene rubber isnot particularly limited, but is preferably from 0.02 to 4.0 mol %, andmore preferably from 0.04 to 3.0 mol %.

Here, “degree of modification” refers to the proportion (mol %) of thedouble bonds modified with a nitrone compound to all the double bondscontained in the butadiene rubber. For example, if the butadiene is1,3-butadiene, a degree of modification is the proportion of formationof the structure represented by Formula (4) or (5) above, via themodification with a nitrone compound. The degree of modification, forexample, can be determined by NMR measurement of the butadiene rubberabove and the nitrone-modified butadiene rubber (i.e., the butadienerubber before and after modification).

It should be noted that a nitrone-modified butadiene with 100 mol % of adegree of modification is also classified as a diene rubber in thepresent disclosure.

As stated above, the content of the nitrone-modified butadiene rubber inthe diene rubber is 15 to 70 mass %. In particular, the content of thenitrone-modified butadiene rubber is preferably 40 mass % or greater.

If the content of the nitrone-modified butadiene rubber in the dienerubber is out of the 15 to 70 mass % range, the energy-saving propertiesor tear resistance and bending resistance are insufficient.

Carbon Black

The carbon black contained in the composition of the present technologyis not particularly limited and, for example, carbon blacks with variousgrades, such as SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, IISAF-HS, HAF-HS,HAF, HAF-LS, FEF, GPF, or SRF can be used. Among these, HAF or GPF ispreferable.

The nitrogen adsorption specific surface area (N₂SA) of the carbon blackis not particularly limited, but is preferably from 25 to 100 m²/g.

Note that the nitrogen adsorption specific surface area (N₂SA) is avalue of the amount of nitrogen adsorbed to the surface of carbon black,measured in accordance with JIS (Japanese Industrial Standard)K6217-2:2001 (Part 2: Determination of specific surface area—Nitrogenadsorption methods—Single-point procedures).

The content of the carbon black in the composition of the presenttechnology is not particularly limited, but is preferably from 20 to 50parts by mass, per 100 parts by mass of the diene rubber describedabove.

Other Components: Optional Components

The composition of the present technology may include other componentssuch as silica, a silane coupling agent, a vulcanization agent, avulcanization aid, or a vulcanization retarder and, furthermore, mayinclude various compounding agents as long as they will not impair theobjective of the present technology.

Silica

The silica is not particularly limited and examples thereof include afumed silica, a calcined silica, a precipitated silica, a pulverizedsilica, a molten silica, a silica anhydride fine particle, a hydratedsilicic acid fine particle, hydrated aluminum silicate, and a hydratedcalcium silicate. One type of these materials can be used alone or twoor more types can be used in combination.

Silane Coupling Agent

The silane coupling agent is not particularly limited, but is preferablya polysulfide-based silane coupling agent used for rubbers.

Among the polysulfide-based silane coupling agents, specific examplesinclude bis(3-triethoxysilylpropyl)tetrasulfide andbis(3-(triethoxysilyl)propyl) disulfide are preferable.

Vulcanization Agent

The vulcanization agent is not particularly limited, and examplesinclude sulfur, organic peroxide-based, metal oxide-based, phenolicresin, and quinone dioxime.

Examples of sulfur include powdered sulfur, precipitated sulfur, highlydispersible sulfur, surface treated sulfur, insoluble sulfur,dimorpholine disulfide, and alkylphenol disulfide.

Examples of organic peroxide vulcanization agents include benzoylperoxide, t-butyl hydroperoxide, 2,4-dichlorobenzoyl peroxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and2,5-dimethylhexane-2,5-di(peroxyl benzoate).

Examples of other vulcanization agents include magnesium oxide,litharge, p-quinone dioxime, p-dibenzoylquinone dioxime,poly-p-dinitrosobenzene, and methylenedianiline.

Vulcanization Aid

As a vulcanization aid, a conventional aid for a rubber can be used incombination. For example, zinc oxide, stearic acid, oleic acid and theirZn salts or the like can be used.

Vulcanization Retarder

Specific examples of the vulcanization retarder include organic acidssuch as phthalic anhydride, benzoic acid, salicylic acid, andacetylsalicylic acid; nitroso compounds such as N-nitroso-diphenylamine,N-nitroso-phenyl-β-naphthylamine, andN-nitroso-trimethyl-dihydroquinoline polymer; halides such astrichloromelanine; 2-mercaptobenzimidazole, and Santogard PVI.

Examples of the compounding agents include fillers other than the carbonblack, antiaging agents, antioxidants, pigments (dyes), plasticizers,thixotropic agents, UV absorbents, flame retardants, solvents,surfactants (including leveling agents), dispersants, dehydratingagents, anticorrosive agents, adhesion promoters, antistatic agents, andprocessing aid.

For these compounding agents, agents generally used for a rubbercomposition may be used. The compounding amounts of such compoundingagents are not particularly limited and can be selected as appropriate.

Method for Producing the Rubber Composition for a Conveyor Belt

The method for producing the composition of the present technology isnot particularly limited, and specific examples thereof include a methodwhereby each of the above-mentioned components is kneaded using apublicly known method and device (e.g. Banbury mixer, kneader, androll). If the composition of the present technology contains sulfur or avulcanization accelerator, the components other than the sulfur and thevulcanization accelerator are preferably blended first at hightemperatures (for example, 40° C. to 160° C.), then cooled, before thesulfur and the vulcanization accelerator are blended.

In addition, the composition of the present technology can be vulcanizedor crosslinked under conventional, publicly known vulcanizing orcrosslinking conditions.

Conveyor Belt

The conveyor belt of the present technology is a conveyor belt in whichthe composition of the present technology is used.

Preferable embodiments of the conveyor belt of the present technologyinclude, for example, a conveyor belt which includes an upper coverrubber layer, a reinforcing layer and a lower cover rubber layer, andthe composition of the present technology is used at least in the lowercover rubber layer.

The preferable embodiment of the conveyor belt of the present technologywill be described below using FIG. 1.

FIG. 1 is a cross-sectional view of a conveyor belt illustrating anexample of the preferable embodiment of the present technology. In FIG.1, the constituting parts are: conveyor belt 1; upper cover rubber layer2; reinforcing layer 3; lower cover rubber layer 4; conveying face fortransporting articles 5; outer layers 11 and 16; and inner layers 12 and15.

As illustrated in FIG. 1, the reinforcing layer 3 is a center layer inthe conveyor belt 1, and the upper cover rubber layer 2 and the lowercover rubber layer 4 are disposed on each side of the reinforcing layer3. The upper cover rubber layer 2 is configured with two layers, theouter layer 11 and the inner layer 12. The lower cover rubber layer 4 isconfigured with two layers, the outer layer 16 and the inner layer 15.The outer layers and the inner layers in the upper cover rubber layer 2and the lower cover rubber layer 4 (the outer layer 11 and the innerlayer 12, the outer layer 16 and the inner layer 15, respectively) maybe independently formed from different rubber compositions.

In FIG. 1, the upper cover rubber layer 2 is configured with two layers,the outer layer 11 and the inner layer 12. However, the number of thelayers that configure the upper cover rubber layer 2 is not limited totwo; it may be one or three or greater. Also, if the number of thelayers that configure the upper cover rubber layer is three or greater,these layers may be independently formed from different rubbercompositions. The same description applies to the lower cover rubberlayer 4.

The outer layer 11 that configures the conveying face for transportingarticles 5 of the upper cover rubber layer 2 is preferably formed from arubber composition that has superior heat resistance, wear resistance,oil resistance and the like. In addition, the inner layer 12 of theupper cover rubber layer 2 contributes to adhesion between thereinforcing layer 3 and the outer layer 11. Therefore, the upper coverrubber layer 2 is preferably configured with two layers of the outerlayer and the inner layer.

The outer layer 16 that configures the back surface of the lower coverrubber layer 4 is formed from the composition of the present technologydescribed above. The inner layer 15 of the lower cover rubber layer 4 ispreferably formed from a rubber composition other than the compositionof the present technology, because of emphasis on production cost andadhesion to the reinforcing layer 3. Therefore, the lower cover rubberlayer 4 is preferably configured with two layers.

A core body of the reinforcing layer 3 is not particularly limited and amaterial generally used for a conveyor belt can be selected for use asappropriate. Specific examples thereof include: a material made of acotton cloth and a chemical fiber or a synthetic fiber, coated andpermeated with a rubber paste; a material enfolded with a cotton clothand a chemical fiber or a synthetic fiber, subjected to RFL treatment; aspecial weave nylon canvas, and steel cords. One type of these can beused alone or two or more types can be laminated for use.

The shape of the reinforcing layer 3 is not particularly limited. Thereinforcing layer 3 can be a sheet-shape as illustrated in FIG. 1, orwire-shaped reinforcing strips arranged in parallel.

A rubber composition that forms the inner layer 12 of the upper coverrubber layer 2 and the inner layer 15 of the lower cover rubber layer 4is not particularly limited and a rubber composition generally used fora conveyor belt may be selected for use as appropriate. One type ofrubber compositions may be used alone or two or more types may be usedas a blend.

A rubber composition that forms the outer layer 11 of the upper coverrubber layer 2 is not particularly limited and a rubber compositiongenerally used for a conveyor belt may be selected for use according tobasic characteristics required for the outer layer (such as heatresistance, wear resistance, and oil resistance, for example) asappropriate.

A thickness of the lower cover rubber layer 4 is preferably 3 to 20 mmand more preferably 5 to 15 mm. The thickness of the lower cover rubberlayer 4 herein is a total of the thickness of inner layer 15 and thethickness of the outer layer 16, if the lower cover rubber layer 4 isconfigured with these layers.

If the thickness of the lower cover rubber layer 4 is within this range,cupping of the belt induced by the degradation of rubber and the likecan be prevented even when the conveyor belt is used for transportationof transportation articles at high temperatures.

Examples

Hereinafter, the present technology will be further described in detailwith reference to examples; however, the present technology is notlimited thereto.

Synthesis of Nitrone Compound

In a 2 L eggplant-shaped flask, methanol heated to 40° C. (900 mL) wasloaded, and then terephthalaldehydic acid represented by Formula (b-1)below (30.0 g) was added and dissolved. To this solution, a solution, inwhich phenylhydroxylamine represented by Formula (a-1) below (21.8 g)was dissolved in methanol (100 mL), was added and stirred at roomtemperature for 19 hours. After the completion of stirring,carboxynitrone (41.7 g) represented by Formula (c-1) below was obtainedby recrystallization from methanol. The yield was 86%.

Synthesis of Nitrone-Modified Butadiene Rubber

The butadiene rubber (NIPOL BR1220, manufactured by Nihon Zeon Corp.)was introduced in a Banbury mixer at 120° C. and kneaded raw for twominutes. Then, one part by mass of the nitrone compound synthesized asdescribed above was introduced into 100 parts by mass of the butadienerubber and the mixture was blended for 5 minutes at 160° C. Thus, thebutadiene rubber was modified with the nitrone compound. Thus, thenitrone-modified butadiene rubber was obtained.

The obtained nitrone-modified butadiene rubber was measured by NMR andthe degree of modification of the nitrone-modified butadiene rubber wasfound to be 0.1 mol %. Specifically, the degree of modification wasdetermined as described below. Namely, the butadiene rubbers before andafter modification were measured for the peak area at around 8.08 ppm(assigned to two protons adjacent to the carboxy group) via ¹H-NMR(CDCl₃, 400 MHz, TMS) using CDCl₃ as a solvent to find the degree ofmodification. Note that the samples used in the ¹H-NMR measurement ofthe nitrone-modified butadiene rubber were dissolved in toluene,purified by methanol precipitation 2 times, and then dried under reducedpressure.

Preparation of Rubber Composition for Conveyor Belt

The components shown in Table 1 below were blended in the proportions(parts by mass) shown in Table 1.

Specifically, the components shown in Table 1 below except from sulfurand the vulcanization accelerator were first mixed in a Banbury mixerfor 5 minutes at 60° C. Thereafter, a roll was used to mix in the sulfurand the vulcanization accelerator to obtain each rubber composition fora conveyor belt (also referred to as “rubber composition” hereinafter).

Evaluation of Energy-Saving Properties

The obtained rubber composition was vulcanized at 148° C. for 30 minutesto prepare a vulcanized rubber composition. Thereafter, the preparedvulcanized rubber composition was cut into a strip shape (length 20mm×width 5 mm×thickness 2 mm) and was prepared as a test piece.

For the obtained test piece, tan δ was measured by a viscoelasticspectrometer (manufactured by Toyo Seiki Seisaku-sho, Ltd.). Themeasurement temperatures were at −40° C. and 20° C. The measurement oftan δ was performed under the condition that the test piece was at 10%stain, and subjected to a vibration at ±2% amplitude and a frequency of20 Hz.

The results are shown in Table 1 (tan δ (−40° C.), tan δ (20° C.)). Theresults were indicated by indices: for Comparative Examples 2 to 3 andWorking Examples 1 to 2, all the indices were normalized to tan δ ofComparative Example 1 as 100.0; for Working Example 3, the index wasnormalized to tan δ of Comparative Example 4 as 100.0.

Smaller tan δ indicates superior energy-saving properties.

Evaluation of Tear Resistance

The vulcanized rubber composition was prepared in the same manner as inthe evaluation of tan δ. A test piece was cut out into a crescent shapefrom each vulcanized rubber composition prepared, in accordance with JISK6252:2001, and a cut with a length of 1.0±0.2 mm was made in adirection perpendicular to the main axis in a central concave part. Thetest was performed in a condition where the travel velocity of a testpiece gripper was at 500 mm/min, and the tear strength (TR) [kN/m] wasmeasured at room temperature.

The results are shown in Table 1 (tear resistance). The results wereindicated by indices: for Comparative Examples 2 to 3 and WorkingExamples 1 to 2, all the indices were normalized to tear strength ofComparative Example 1 as 100.0; for Working Example 3, the index wasnormalized to tear strength of Comparative Example 4 as 100.0.

Greater tear strength indicates superior tear resistance.

Evaluation of Bending Resistance

According to the flex crack growth test in accordance with JISK6260:2010, crack generation test was performed by repeated bending.

Specifically, a vulcanized rubber composition was prepared in the samemanner as in the evaluation of tan δ as described above, and a testpiece of the size and the thickness defined in the flex crack growthtest above was prepared. Then, the test was performed using a De Mattiaflex test machine for a test piece with a cut made by a designated blade(temperature: room temperature, stroke: 20 mm, number of bending perminute: 300±10). The crack length after 400,000 bendings was recorded.

The results are shown in Table 1 (bending resistance). The results wereindicated by indices: for Comparative Examples 2 to 3 and WorkingExamples 1 to 2, all the indices were normalized to the crack length ofComparative Example 1 as 100.0; for Working Example 3, the index wasnormalized to the crack length of Comparative Example 4 as 100.0.

Shorter crack length indicates superior bending resistance.

TABLE 1 Comparative Comparative Comparative Example 1 Example 2 Example3 NR 40.00 40.00 40.00 BR 60.00 50.00 Terminal-modified BR 60.00Nitrone-modified BR 10.00 Carbon black 1 37.00 37.00 37.00 Carbon black2 Silica Sulfur 1.50 1.50 1.50 Vulcanization accelerator 1.50 1.50 1.50tan δ (−40° C.) 100.0 112.9 97.1 tan δ (20° C.) 100.0 77.1 97.6 Tearresistance 100.0 28.0 104.0 Bending resistance 100.0 600.0 87.7 WorkingWorking Comparative Working Example 1 Example 2 Example 4 Example 3 NR40.00 40.00 70.00 70.00 BR 30.00 30.00 Terminal-modified BRNitrone-modified BR 30.00 60.00 30.00 Carbon black 1 37.00 37.00 Carbonblack 2 30.00 30.00 Silica 10.00 10.00 Sulfur 1.50 1.50 3.00 3.00Vulcanization 1.50 1.50 1.50 1.50 accelerator tan δ (−40° C.) 91.1 87.9100.0 88.0 tan δ (20° C.) 92.6 89.0 100.0 94.4 Tear resistance 112.1120.8 100.0 102.1 Bending resistance 70.0 10.0 100.0 86.5

The details of each component shown in Table 1 above are as follows.

-   -   NR: Natural rubber; RSS #3    -   BR: Butadiene rubber: Nippol BR 1220 (manufactured by the Zeon        Corporation)    -   Terminal-modified BR: Terminal-modified butadiene rubber, Nipol        BR 1250H (manufactured by Zeon Corporation)    -   Nitrone-modified BR: Nitrone-modified butadiene rubber        synthesized as described above    -   Carbon black 1: HAF-grade carbon black, Show Black N339        (nitrogen adsorption specific surface area=90 m²/g, manufactured        by Cabot Japan)    -   Carbon black 2: GPF-grade carbon black, Diablack G (nitrogen        adsorption specific surface area=29 m²/g, manufactured by        Mitsubishi Chemical Corporation)    -   Silica: Precipitated silica, Nipsil AQ (manufactured by Tosoh        Silica Corporation)    -   Sulfur: Oil-treated sulfur (manufactured by Hosoi Chemical        Industry Co., Ltd.)    -   Vulcanization accelerator: N-tert-butyl-2-benzothiazolyl        sulfenamide, NOCCELER NS-P (manufactured by Ouchi Shinko        Chemical Industrial Co., Ltd.)

As can be seen from Table 1, all of the working examples of the presentapplication, which contained the nitrone-modified butadiene rubber,exhibited superior energy-saving properties, tear resistance and bendingresistance, compared to Comparative Examples 1, 2 and 4, which do notcontain the nitrone-modified butadiene rubber.

Comparison between Working Examples 1 and 2 showed that Working Example2 which contained the nitrone-modified butadiene rubber at 40 mass % orgreater in the diene rubber exhibited superior energy-saving properties,tear resistance and bending resistance.

Comparative Example 3, which contained the nitrone-modified butadienerubber but the content of the nitrone-modified butadiene rubber in thediene rubber was less than 15 mass %, exhibited insufficientenergy-saving properties.

1. A rubber composition for a conveyor belt comprising: a diene rubber and a carbon black, the diene rubber containing: a natural rubber; and a modified butadiene rubber obtained by modifying a butadiene rubber with a nitrone compound; a content of the natural rubber in the diene rubber being 30 to 85 mass %, and a content of the modified butadiene rubber in the diene rubber being 15 to 70 mass %.
 2. The rubber composition for a conveyor belt according to claim 1, wherein the nitrone compound contains a carboxy group.
 3. The rubber composition for a conveyor belt according to claim 1, wherein a content of the carbon black is from 20 to 50 parts by mass per 100 parts by mass of the diene rubber.
 4. The rubber composition for a conveyor belt according to claim 1, wherein a nitrogen adsorption specific surface area of the carbon black is from 25 to 100 m²/g.
 5. The rubber composition for a conveyor belt according to claim 1, wherein the nitrone compound is a compound selected from the group consisting of N-phenyl-α-(4-carboxyphenyl)nitrone, N-phenyl-α-(3-carboxyphenyl)nitrone, N-phenyl-α-(2-carboxyphenyl)nitrone, N-(4-carboxyphenyl)-α-phenylnitrone, N-(3-carboxyphenyl)-α-phenylnitrone, and N-(2-carboxyphenyl)-α-phenylnitrone.
 6. The rubber composition for a conveyor belt according to claim 1, wherein a degree of modification of the modified butadiene rubber is from 0.02 to 4.0 mol %, where “degree of modification” refers to a proportion (mol %) of double bonds modified with the nitrone compound to all the double bonds contained in the butadiene rubber.
 7. A conveyor belt comprising the rubber composition for a conveyor belt described in claim 1 as a lower cover rubber layer.
 8. The rubber composition for a conveyor belt according to claim 2, wherein a content of the carbon black is from 20 to 50 parts by mass per 100 parts by mass of the diene rubber.
 9. The rubber composition for a conveyor belt according to claim 2, wherein a nitrogen adsorption specific surface area of the carbon black is from 25 to 100 m²/g.
 10. The rubber composition for a conveyor belt according to claim 3, wherein a nitrogen adsorption specific surface area of the carbon black is from 25 to 100 m²/g.
 11. The rubber composition for a conveyor belt according to claim 8, wherein a nitrogen adsorption specific surface area of the carbon black is from 25 to 100 m²/g.
 12. The rubber composition for a conveyor belt according to claim 2, wherein the nitrone compound is a compound selected from the group consisting of N-phenyl-α-(4-carboxyphenyl)nitrone, N-phenyl-α-(3-carboxyphenyl)nitrone, N-phenyl-α-(2-carboxyphenyl)nitrone, N-(4-carboxyphenyl)-α-phenylnitrone, N-(3-carboxyphenyl)-α-phenylnitrone, and N-(2-carboxyphenyl)-α-phenylnitrone.
 13. The rubber composition for a conveyor belt according to claim 3, wherein the nitrone compound is a compound selected from the group consisting of N-phenyl-α-(4-carboxyphenyl)nitrone, N-phenyl-α-(3-carboxyphenyl)nitrone, N-phenyl-α-(2-carboxyphenyl)nitrone, N-(4-carboxyphenyl)-α-phenylnitrone, N-(3-carboxyphenyl)-α-phenylnitrone, and N-(2-carboxyphenyl)-α-phenylnitrone.
 14. The rubber composition for a conveyor belt according to claim 4, wherein the nitrone compound is a compound selected from the group consisting of N-phenyl-α-(4-carboxyphenyl)nitrone, N-phenyl-α-(3-carboxyphenyl)nitrone, N-phenyl-α-(2-carboxyphenyl)nitrone, N-(4-carboxyphenyl)-α-phenylnitrone, N-(3-carboxyphenyl)-α-phenylnitrone, and N-(2-carboxyphenyl)-α-phenylnitrone.
 15. The rubber composition for a conveyor belt according to claim 8, wherein the nitrone compound is a compound selected from the group consisting of N-phenyl-α-(4-carboxyphenyl)nitrone, N-phenyl-α-(3-carboxyphenyl)nitrone, N-phenyl-α-(2-carboxyphenyl)nitrone, N-(4-carboxyphenyl)-α-phenylnitrone, N-(3-carboxyphenyl)-α-phenylnitrone, and N-(2-carboxyphenyl)-α-phenylnitrone.
 16. The rubber composition for a conveyor belt according to claim 9, wherein the nitrone compound is a compound selected from the group consisting of N-phenyl-α-(4-carboxyphenyl)nitrone, N-phenyl-α-(3-carboxyphenyl)nitrone, N-phenyl-α-(2-carboxyphenyl)nitrone, N-(4-carboxyphenyl)-α-phenylnitrone, N-(3-carboxyphenyl)-α-phenylnitrone, and N-(2-carboxyphenyl)-α-phenylnitrone.
 17. The rubber composition for a conveyor belt according to claim 10, wherein the nitrone compound is a compound selected from the group consisting of N-phenyl-α-(4-carboxyphenyl)nitrone, N-phenyl-α-(3-carboxyphenyl)nitrone, N-phenyl-α-(2-carboxyphenyl)nitrone, N-(4-carboxyphenyl)-α-phenylnitrone, N-(3-carboxyphenyl)-α-phenylnitrone, and N-(2-carboxyphenyl)-α-phenylnitrone.
 18. The rubber composition for a conveyor belt according to claim 11, wherein the nitrone compound is a compound selected from the group consisting of N-phenyl-α-(4-carboxyphenyl)nitrone, N-phenyl-α-(3-carboxyphenyl)nitrone, N-phenyl-α-(2-carboxyphenyl)nitrone, N-(4-carboxyphenyl)-α-phenylnitrone, N-(3-carboxyphenyl)-α-phenylnitrone, and N-(2-carboxyphenyl)-α-phenylnitrone.
 19. The rubber composition for a conveyor belt according to claim 2, wherein a degree of modification of the modified butadiene rubber is from 0.02 to 4.0 mol %, where “degree of modification” refers to a proportion (mol %) of double bonds modified with the nitrone compound to all the double bonds contained in the butadiene rubber.
 20. The rubber composition for a conveyor belt according to claim 3, wherein a degree of modification of the modified butadiene rubber is from 0.02 to 4.0 mol %, where “degree of modification” refers to a proportion (mol %) of double bonds modified with the nitrone compound to all the double bonds contained in the butadiene rubber. 